Die steel for hot working



Patented J 14, 1942 DIE STEEL FOB. HOT WORKING John Nelson, Oakmont, Pm, asslgn'or to Braeburn Alloy Steel Oorpo corporation of Penny! No Drawing. Application April Serial No. 388,817

ration, Braeburn, Pa., a vania 4 Claims. 148-31) This invention relates to die steels for hot working metals and particularly to die steels for die casting brass. In the die casting of brass, the brass is generally at" a temperature of about 1900 to 1950 C. and is in a liquid or semi-liquid condition. It is cast through dies of alloy steel, which dies must beable to withstand the high temperature without cracking or the formation of hair line cracks known as crazing which if present make imperfections in the casting.' The steel for the dies is made by the steel manufacturer and is sent to the die maker, who machines the steel to form dies of suitable size and shape. It is necessary that the steel received by the. die maker be soft enough so that it can be machined in the making of the dies. 0n the other hand, it is necessary that the dies after machining be capable of being hardened and that this hardened condition be maintained in the use of the dies at high temperatures.

Die steels according to the present invention meet these requirements of being soft enough to machine in the quenched condition and being hard enough after drawing at a lower temperature so that they are eminently suited for the production of dies used in the hot working of metal. The steel when quenched in either air or oil from a temperature of about 2,000 to 2200 F. has a Rockwell C hardness ofabout 34 to 37, so that it can be readily machined to the desired shape in the formation of the dies. The dies may then'be drawn at a temperature of about 1100 to 1250 F. to impart a Rockwell C hardness of about 39 to 43. The dies show very remarkable resistance to crazing and cracking in use at high temperatures and also retain their qualities of hardness and toughness when used at high temperatures. The dies are very resistant to erosion or deformation under repeated strains and long application. The die surfaces remain smooth and polished and even after long use give the proper surface to the casting which is being produced. Theseproperties make the steel use- I ful not only in brass die casting or the die casting of other metals but also in extrusion dies, gripper dies, piercer points for making shells or in fact in any case where the steel is to be subjected in use to high temperatures.

The steel of the present invention contains substantial amount of chromium, tungsten and be considerably better than the same alloy containing high silicon. It is preferred that the steel contain cobalt but the invention contemplates alloys either containing cobalt or not containing it.

The following table gives the ranges of elements covered by my invention. In this table are given a broad range, a preferred range and a specific analysis of the composition.

Table It will be noted that the steel contains both molybdenum and tungsten instead of either one alone since the combination of both of these elements has been found to produce very superior results. The carbon is never over 135% and preferably is between .10 and .20%. It has been thought previously that it was necessary to use a higher carbon content in order to produce the requisite hardness in the alloyw I have found, however, that the required hardness may be obtained while using a low carbon content, provided the other elements are within the ranges given. Lowering of the carbon content reduces the tendency of the die to check or crack, which is a distinct advantage.

Although some of the advantages of my alloy are obtained when the silicon is above .40% and within the range from .10 to 1.25%, the full'advantages of my alloy steel are attained only when both the carbon and the silicon are low. Thus a steel having an analysis conforming to the specific analysis given in the table (carbon .15% and silicon .15%) has proved in actual use to be materially better than a steel of substantially the same analysis except that the silicon was 1.25%.

For best results the carbon should be between molybdenum. The carbon is low and the silicon also is preferably low, as it has been found that low carbon and silicon, along with the substantial amounts of chromium, tungsten and molybdenum produce dies which in use have proved to about .10 and 20% and the silicon should not be over about .40%.

The steel has the property of developing secondary hardness upon drawing to a temperature lower than the temperature at which the steel was quenched. The steel may be heated to about 2000 to 2200 F. and quenched either in air or analysis oil. Steel or" the specific analysis given in the table when quenched in air from about 2100 F. showed a Rockwell C hardness of 34. By drawing this steel at a temperature of about 1150 F., p

the hardness was increased to about 39. This same steel when quenched in oil from a temperature of about2000 F. had a hardness of 34.5 and when drawn at 1150 F. had a hardness of 38.5. By quenching in oil from a temperature of about 2100 F. and drawing at a temperature of about 1150 F. a hardness of 43.5 was obtained. My alloy steel containing both tungsten and molybdenum has proved superior to a similar steel containing only tungsten. Steel of the present invention containing both low carbon and low silicon has proved superior to a similar steel containing high silicon, This is in spite of the fact that it had been previously thought necessary to employ high silicon in a die steel for hot working. The steel of the present invention has the valuable properties of showing very remarkable resistance to crazing or cracking when subjected to high temperatures. It can be quenched to make it soft enough to machine and then hardened by drawing at a lower temperature than the quenching temperature and it retains its hardened condition for long periods of time without crazing or cracking when subjected to high temperatures.

The invention is not limited to the preferred analysis, which has been given merely for illustrative purposes, but may be otherwise embodied or practiced within the scope of the following claims.

Iclaim:

1. A die steel for hot working, comprising about:

Per cent Carbon .10to .20 Silic .1011) .40 Manganese...- .10to .60 Chromium 2.5 to10.0 Tungsten 2.0 to 8.0 Molybdenum 2.0 to 8.0 Vanadium .10 to .60 Cobalt .25t0 2.0

the balance being iron except for incidental impurities.

2. A die steel for hot working, comprising about:

the balance being iron except for incidental impurities, said steel having been heat-treated by quenching in air or oil from about 2000 to 2200 F. and drawn at about 1100 to 1250 F.

3. A die steel for hot working, comprising about:

Per cent Carbon .10to .20 Silicon .10to .40 Manganese .10 to .60 Chromium 2.5 to 10.0 TungsteniL 2.0 to 8.0 Molybdenum 2.0 to 8.0 Vanadium .10 to .60 Cobalt .25t0 2.0

the balance being iron except for incidental impurities, said steel having been heat-treated by quenching in air or oil from about 2000 to 2200 F. and drawn at about 1100 to 1250 F., the steel in said quenched condition having a hardness of about 34 to 37 and in the drawn condition a hardness of about 39 to 43 Rockwell C.

4. A die steel for hot working, comprising about:

. Per cent Carbon .15 Silicon .15 Manganese .26 Chromium 6.21 Tungsten 4.11 Molybdenum 4.23 Vanadium .27 Cobalt .30

the balance being iron except for incidental impurities.

JOHN NELSON. 

